1. Field of the Invention
The present invention relates to an electrophotographic process and an electrophotographic apparatus which can be applicable in copying machines, printers and facsimile machines.
2. Description of the Prior Art
In the practice of the electrophotographic process, a magnetizable developing material, or a developer mix, of a two-component type has been widely utilized, comprising toner particles and carrier beads mixed together in a predetermined proportion. For developing an electrostatic latent image into a visible powder image with the use of the developer mix, various developing methods have hitherto been suggested. However, of them, a magnetic brush developing method developed in 1953 is currently widely utilized for document copying because, as compared with a cascade developing method, the magnetic brush developing method can result in a reduction in size of the apparatus and also in a satisfactory reproduction of fine line images.
Hereinafter, the conventional developing method utilizing the developer mix will be discussed in detail with reference to FIG. 12. FIG. 12 schematically illustrates a prior art electrophotographic apparatus. The illustrated apparatus generally comprises a hopper accommodating therein a mass of the developer mix 1 consisting of a mass of toner material and a mass of carrier. A developing sleeve 2 accommodates therein and is magnet roll 3 therein and positioned inside the hopper. A photoreceptor drum has a photosensitive layer 4 on its outer peripheral surface and is supported for rotation in one direction. A corona charger 5 for electrostatically charges the photosensitive layer 4. A transfer corona charger 7 transfers a visible powder image onto a recording medium such as, for example, a recording paper, and a cleaning unit 8 removes residue toner material from the photosensitive layer 4 on the photoreceptor drum.
The electrophotographic apparatus has a plurality of sequential processing stations. These include a charging station at which the corona charger 5 is disposed. An exposure station projects an imagewise light signal 6 onto the photosensitive layer 4 to form an electrostatic latent image thereon. A developing station develops the electrostatic latent image into the visible powder image by means of the developing sleeve 2. A transfer station at which the transfer corona charger 7 is disposed effects the transfer of the visible powder image onto the recording paper. A separating station separates the recording paper bearing the visible powder image from the photosensitive layer 4 for conveyance towards a fixing unit (not shown), and a cleaning station has the cleaning unit 8 disposed thereat. The photoreceptor drum having the photosensitive layer 4 is moved sequentially past these processing stations during one complete rotation thereof.
As is well known to those skilled in the art, during the rotation of the photoreceptor drum, the photosensitive layer 4 is electrostatically charged by the corona charger 5 at the charging station and is subsequently exposed at the exposure station to the imagewise light signal 6 to form thereon the electrostatic latent image which is developed at the next succeeding developing station into the visible powder image by means of magnetic brushes of the developer mix 1 formed on the developing sleeve 2. This visible powder image is then transferred at the transfer station onto the recording medium.
While during the continued rotation of the photoreceptor drum the recording paper bearing the visible powder image is separated from the photosensitive layer 4 and is thereafter transported towards the fixing unit for permanently fixing the image on the recording paper, residue toner material left on the photosensitive layer 4 is removed therefrom at the cleaning station in readiness for the next cycle of image formation.
The prior art electrophotographic apparatus of the construction described above has a number of problems. In the first place, the developing unit, including the hopper, the developing sleeve 2 and the magnet roll 3, is bulky and complicated, rendering the electrophotographic apparatus as a whole to be complicated and bulky. Also, the length of time during which the magnetic brushes of the developer mix 1 operatively contact the photosensitive layer 4 then moving past the developing station is so small as to eventually result in a poor image quality.